<!DOCTYPE html>
<html>
<head>
	<title>css-dropmenu</title>
	<meta charset="utf-8">
	<style type="text/css">
		.dropdown{
			position: relative;
			display: inline;
			background-color: white;
		}

		.dropdown-content{
			  display: none;
			  position: absolute;
			  background-color: #f9f9f9;
			  min-width: 100px;
			  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
			  padding: 1px 1px;
		}

		.dropdown:hover .dropdown-content{
			display: block;
		}

		.dropdown:active{
			background-color: black;
		}

		ul.a{
			list-style-type: circle;
		}

		.dropbtn{
			background-color:  #4CAF50;
			color: white;
			padding: 12px;
			font-size: 16px;
			border: none;
			cursor: pointer;
		}

		.dropbtn:hover .dropdown-content{
			display: inline-block;
		}
	</style>
</head>
<body>

	<div class="dropdown">
		<span>Mouse over me</span>
		<div class="dropdown-content">
			<ul class="a">
				<li>Helloworld</li>
				<li>Helloworld</li>
				<li>Helloworld</li>
				<li>Helloworld</li>
			</ul>
		</div>
	</div>

	<div>
		<button class="dropbtn">下拉菜单</button>
	</div>
</body>
</html>